Do you mean the "Collection" edition bumper, as pictured in my avatar to the left? Batinc.net has them, and they are located in Florida. I got mine from ZX3tuning last summer. They are in British Columbia, Canada I believe. You might also check them out.
If you're talking about the bumper that comes on the Focus RS (wider, to accomodate fender flares), then I don't know of anyone in the U.S. that stocks them. www.european-parts.net in Germany (they will ship to the U.S.) has them though, for a mighty price.